1. Field of the Invention
The present invention relates generally to an actively controlled automotive suspension system, in which suspension characteristics is adjusted in active manner for suppressing attitude change of a vehicle body. More particularly, the invention relates to an actively controlled suspension system which performs anti-rolling and/or anti-pitching suspension control depending upon the vehicle driving condition. Further particularly, the invention relates to an actively controlled suspension system which make a vehicular driver to easily recognize critical vehicular driving condition during cornering and/or braking and thus avoid to cause sudden break of suspension which brings significant change of vehicular attitude.
2. Description of the Background Art
The U.S. Pat. No. 4,702,490, issued on Oct. 27, 1987, to Hirotsugu YAMAGUCHI et al., and assigned to the common assignee to the present invention, discloses an actively or positively controlled automotive suspension system which includes hydraulic cylinder for generating variable damping force against relative motion of a vehicular suspension member and a vehicle body in bounding and rebounding directions for adjusting suspension characteristics and adjusting vehicle body attitude.
Similar type actively controlled suspension systems has been disclosed in the U.S. Pat. No. 4,801,155 assigned to the common assignee to the present invention, European Patent First Publications Nos. 02 49 246 and 02 49 209 respectively corresponding to co-pending U.S. Pat. Applications Ser. Nos. 061,368 (filed on June 15, 1987) and 059,888, filed on June 9, 1987, both of which have been assigned to the common assignee to the present invention. The later-mentioned three inventions include features of anti-rolling and/or anti-pitching suspension control for adjusting damping characteristics at respective vehicular wheel for suppressing vehicular rolling motion.
Furthermore, U.S. Pat. No. 4,865,347, U.S. Pat. No. 4,888,696 and U.S. Pat. No. 4,872,701 are also assigned to the common assignee to the present invention. These co-pending applications disclose actively controlled suspension systems which are provided variable suspension characteristics with variable sensibility for vehicular body attitude change.
Such prior proposed suspension control systems are satisfactorily systems for achieving riding comfort and driving stability and for successfully suppressing attitude change. However, despite effectiveness in anti-rolling and anti-pitching control in the prior proposed suspension control systems, vehicular suspension tends to break traction to cause uncontrollable attitude change when acceleration, i.e. lateral or longitudinal acceleration, exerted on the vehicle body becomes greater than a predetermined value which may be determined according to setting of suspension of respective individual vehicles. As long as the anti-rolling and anti-pitching control are effective in the suspension control system, the driver cannot recognize that he is driving the vehicle near the vehicular critical condition, i.e. the acceleration exerted on the vehicular body being large enough to be near mechanical and/or hydraulical setting of the suspension system until suspension breaks traction. Breakage of traction causes sudden and substantial change of vehicular attitude to make the vehicle unstable condition.